<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>开关灯</title>
</head>
<body>
<button onclick="document.getElementById('demo').src='开灯.png'" > 开灯</button>
<img  id="demo" src="关灯.png" style="text-align: center">
<button onclick="document.getElementById('demo').src='关灯.png'"> 关灯</button>
</body>
</html>